The present invention relates generally to internal combustion engines and relates more particularly to a fuel injection pump for use with diesel engine fuel injection systems.
Diesel engines due to their weight, cost, sluggish acceleration and noisy operation have in the past been utilized primarily for commercial applications such as trucks, locomotives, ships and stationary engines wherein their reliability, durability and economy of operation are of paramount importance. In recent years, however, the diesel engine has become more acceptable for use in light duty vehicles such as automobiles and small trucks, small tractors and the like. This acceptance has been due largely to the scarcity and high cost of gasoline, the excellent fuel economy of the diesel engine and the development of quieter diesel engines.
A common approach in light duty diesel engine design has been to utilize some type of precombustion chamber into which the fuel is injected. Although the fuel injection in the precombustion chamber type engines is less critical due to the turbulence effects which are designed to break up and disperse the injected fuel, the engine operating economy is somewhat lower than with the open chamber type engine.
In view of the urgent need to produce diesel engines having the maximum possible fuel economy, designers are turning toward the open chamber engine design for light duty diesel engines despite the more critical fuel injection requirements of such engines. In particular, the open chamber engines require much higher fuel injection pressures to provide a sufficient fuel atomization and dispersion within the combustion chamber. With the precombustion chamber type engines, fuel injection pressures of 2,000 to 4,000 psi have been adequate whereas with the open chamber type engine design, injection pressures on the order of 10,000 to 12,000 psi are required for efficient operation.
A known form of fuel injection pump for light duty diesel service is the opposed plunger rotary distributor type pump wherein the fuel pumping is effected by two or more opposed pistons disposed within a rotating member with the piston being moved radially inwardly by the engagement of the piston tappet assemblies with the lobes of an internal ring cam. This type of pump provides a relatively simple, compact pump which has been adequate for the low pressure demands of many light-duty diesel engines. In its usual form, such a pump is not suited for high pressure injection service, in large measure due to the fuel metering arrangement which is of the so-called "inlet metering" type. In this arrngement, the pumping pistons are displaced during their fill cycle only an amount sufficient to introduce the metered fuel quantity into the pumping chamber. As a result, the pumping is effected only on the downward side of the piston velocity curve with the result that the flow rate and hence the pressure developed by the pump is of a relatively low order, generally under 4,000 psi.